The present invention relates to a radar device having means for generating a first code, means for modulating a transmission signal in a transmitting branch using the first code, means for delaying the first code, means for modulating a signal in a receiving branch using the delayed first code, and means for mixing a reference signal with a reception signal. The present invention further relates to a method of coding a radar device having the following steps: generating a first code, modulating a transmission signal in a transmitting branch using the first code, delaying the first code, modulating a signal in a receiving branch using the delayed first code, and mixing a reference signal with a reception signal.
There are numerous applications for radar devices in greatly varying fields of technology. For example, it is possible to use radar sensors for local range sensor systems in motor vehicles.
Electromagnetic waves are emitted from a transmission antenna in radar devices. If these electromagnetic waves encounter a barrier, they are reflected and, after the reflection, received again by another antenna or the same antenna. Subsequently, the signals received are fed to a signal processing and signal analysis system.
In motor vehicles, radar sensors are used for measuring the distance to targets and/or the relative speed in relation to such targets outside the motor vehicle. Vehicles which are traveling ahead or parking are considered targets, for example.
FIG. 1 shows a schematic illustration of a radar device having a correlation receiver according to the related art. A transmitter 300 is caused by a pulse generator 302 to emit a transmission signal 306 via an antenna 304. Transmission signal 306 encounters a target object 308, where it is reflected. Reception signal 310 is received by antenna 312. This antenna 312 may be identical to antenna 304. After reception signal 310 is received by antenna 312, the signal is transferred to receiver 314 and subsequently fed via a unit 3 having a low-pass filter and an analog/digital converter, to a signal analysis system 318. The special feature of the correlation receiver is that receiver 314 obtains a reference signal 320 from pulse generator 302. Reception signals 310 received by receiver 314 are mixed in receiver 314 with reference signal 320. Receiver 314 may contain an inphase/quadrature (I/Q) demodulator. Through the correlation, the distance to a target object, for example, may be determined on the basis of the time delay from transmission to reception of the radar pulse.
It is desirable to separate interference signals, which arise, for example, from other transmitter antennas, from signal components reflected on the targets. Interference is generated, for example, by other radar sensors, transmitters, consumers on the vehicle electrical system of the motor vehicle, mobile telephones, or by noise. Conventional methods use additional modulation of signals in order to separate interference signals from signal components reflected on targets. Using pseudo-noise coding (PN coding) for interference signal suppression has also already been suggested. Minimizing this type of interference is to be achieved through coding, with the signal-to-noise ratio (S/N) in the output signal of the radar device possibly enhanced. Through such an enhancement of the S/N ratio, either detecting targets having smaller retroreflection cross-sections or reducing the peak pulse power at constant S/N is made possible. The advantage of detecting targets having smaller retroreflection cross-sections is, for example, that not only motor vehicles traveling ahead, but also pedestrians or bicyclists, are detected by a motor vehicle with greater probability. The reduction of the peak pulse power has the consequence that less interference is caused in other systems, for example, radio relay systems; in this connection, the reduction of the peak pulse power makes approval of the sensors by the relevant regulating authorities easier.
Furthermore, when multiple radar sensors are used, the aim is to receive and analyze the transmission signals of the respective other sensors. Therefore, one wishes to be able to differentiate between the signals of other radar sensors.
The present invention is based on the radar device provided with multiple receiving channels. The receiving channels have means for generating additional codes, means for demodulating using the respective additional codes, and means for modulating the transmission signal using at least one of the additional codes. In this way, it is possible to differentiate between the signals of multiple radar sensors. Therefore, an improvement of the interference signal suppression and/or an enhancement of the S/N ratio occurs through the modulation of the signals with a decoupling of various radar sensors by using different codes. In this manner, the detection of apparent targets may be suppressed, and the target geometry may be determined more precisely.
One of the signals is preferably modulated using the first code through amplitude modulation (ASK; xe2x80x9camplitude shift keyingxe2x80x9d) and the other signal is modulated using the first code through phase modulation (PSK; xe2x80x9cphase shift keyingxe2x80x9d). It is also possible to combine amplitude modulation with phase modulation, so that different types of modulation are usable in the scope of an exemplary embodiment of the present invention. It is also possible to use frequency modulation (FSK; xe2x80x9cfrequency shift keyingxe2x80x9d).
In the present invention, the transmission signal may be modulated using the first code through phase modulation (PSK) and the signal is modulated in the receiving branch using the first code through amplitude modulation (ASK) or frequency modulation (FSK). If types of modulation other than phase modulation (PSK) are used in the receiving branch, then phase modulation (PSK) may be used in the transmitting branch in the scope of an exemplary embodiment of the present invention.
However, it may also be advantageous for the transmission signal to be modulated using the first code through amplitude modulation (ASK), frequency modulation (FSK) or phase modulation (PSK), and for the signal to be modulated in the receiving branch using the first code through phase modulation (PSK). Therefore, if there is phase modulation (PSK) in the receiving branch, then greatly varying types of modulation are usable in the transmitting branch.
The radar device is particularly advantageously refined if one of the combinations of types of modulation cited is used for the additional codes independently of the types of modulation used for the first code.
A low-pass filter is preferably provided for filtering the signals before demodulation. In this manner, it is possible to use a low clock frequency for the additional codings. This particularly may have the advantage that the coding in the receiving channels does not have to be delayed. Implementation of a very large number of channels with only a low additional outlay for components is possible, these components being clocked using relatively low frequencies. On the high-frequency domain, only one additional modulation must be provided, possibly through an additional modulator. The implementation of the receiving channels on the low-frequency domain also has the advantage that there is no worsening of the S/N ratio.
It may be advantageous if the code is a pseudo-noise code (PN code). The use of PN codes for interference signal suppression has been extensively described in the literature, so that an exemplary embodiment of the present invention may be realized particularly well using PN codes.
The generation of the additional codes and the modulation are preferably performed using a clock frequency which is a whole-number fraction of the pulse repetition frequency for generating the first code. In this way, the code generations a to one another with regard to the various codes.
It is preferable for k receiving channels to be provided, for k means for generating k additional codes to be provided, and for each of the k additional codes to be orthogonal to each of the other kxe2x88x921 additional codes. Due to the orthogonality of the codes, it is possible, in the event of overlapping detection ranges of the respective sensors, to analyze only the appropriate sensors in a respective receiving channel. Furthermore, the circuits for orthogonal codes are simpler to produce.
A counter and multiple EXOR gates are provided for generating the orthogonal codes. In this way, ideal decouplings of the respective radar sensors may be generated, for example through cyclic inversion.
A toggle flipflop (TFF) and an EXOR gate are provided for generating the orthogonal codes. Two orthogonal codes may be generated in a particularly simple way by one TFF.
In this connection, PSK may be used in the receiving branch, an uncoded receiving channel may be additionally provided. Using a TFF and an EXOR gate, the implementation of three receiving channels is therefore possible due to the additional uncoded receiving channel.
Digital means are preferably provided for controlling the delay. These types of digital means, for example a microcontroller or a digital signal processor, are capable of delaying both the pulse repetition frequency and the PN code in a suitable way, so that the signals experience the possibly necessary correlation in the receiving branch.
However, it may also be advantageous if circuit means are provided for controlling the delay. In addition to controlling the delay using digital means, it is therefore also possible to use hardware to implement the delay.
Means may be provided for blanking phase transitions. Since the switchover of the phase angle does not occur instantaneously in the real construction, errors arise after the integration of the signal. If, however, the phase-modulated signal is blanked during the transition time between the various phase angles, these errors may be minimized.
An exemplary embodiment of the present invention builds on the method in that multiple receiving channels are provided, additional codes are generated in the receiving channels, signals are modulated in the receiving channels using the respective additional codes, and the transmission signal is modulated using at least one of the additional codes. In this way it is possible to differentiate between the signals of multiple radar sensors. Therefore, an improvement of the interference signal suppression and/or an enhancement of the S/N ratio occurs through the modulation of the signals with a decoupling of various radar sensors by using different codes. In this manner, the detection of apparent targets may be suppressed, and the target geometry may be determined more precisely.
It is particularly preferred if one of the signals is modulated using the first code through amplitude modulation (ASK; xe2x80x9camplitude shift keyingxe2x80x9d) and the other signal is modulated using the first code through phase modulation (PSK; xe2x80x9cphase shift keyingxe2x80x9d). It is also possible to combine amplitude modulation with phase modulation, so that different types of modulation are usable in the scope of the present invention. It is also possible to use frequency modulation (FSK; xe2x80x9cfrequency shift keyingxe2x80x9d).
It is possible for the transmission signal to be modulated using the first code through phase modulation (PSK) and for the signal to be modulated in the receiving branch using the first code through amplitude modulation (ASK) or frequency modulation (FSK; xe2x80x9cfrequency shift keyingxe2x80x9d). If types of modulation other than phase modulation (PSK) are used in the receiving branch, then phase modulation (PSK) is used in the transmitting branch in the scope of an exemplary embodiment of the present invention.
The transmission signal may be modulated using the first code through amplitude modulation (ASK), frequency modulation (FSK) or phase modulation (PSK), and the signal may be modulated in the receiving branch using the first code through phase modulation (PSK). Therefore, if there is phase modulation (PSK) in the receiving branch, then greatly varying types of modulation are usable in the transmitting branch.
In an exemplary method according to the present invention, one of the combinations of types of modulation cited is used for the additional codes independently of the types of modulation used for the first code.
The signals may be filtered in a low-pass filter before demodulation. In this manner, it is possible to use a low clock frequency for the additional codings. This may have the advantage that the coding in the receiving channels does not have to be delayed. Implementation of a very large number of channels with only a low additional outlay for components is possible, these components being clocked using relatively low frequencies. On the high-frequency domain, only one additional modulation must be provided, possibly through an additional modulator. The implementation of the receiving channels on the low-frequency domain also has the advantage that there is no worsening of the S/N ratio.
The codes are preferably pseudo-noise codes (PN codes). The use of PN codes for interference signal suppression has been extensively described in the literature, so that an exemplary embodiment of the present invention may be realized particularly using PN codes.
In an exemplary embodiment of the present invention, the generation of the additional codes and the demodulation may be performed using a clock frequency which is a whole-number fraction of the pulse repetition frequency for generating the first PN code. In this way, the code generations and the demodulations are adapted to one another with regard to the various codes.
It may be possible for k receiving channels to be provided, for k means for generating k additional codes to be provided, and for each of the k additional codes to be orthogonal to each of the other kxe2x88x921 additional codes. Due to the orthogonality of the codes, it may be possible, in the event of overlapping detection ranges of the respective sensors, to analyze only the appropriate sensors in a respective receiving channel. Furthermore, the circuits for orthogonal codes may be simpler to produce.
The orthogonal codes may be generated by a counter and multiple EXOR gates. In this manner decouplings of the respective radar sensors may be generated, for example, through cyclic inversion.
In an exemplary embodiment, the orthogonal codes are generated by a toggle flipflop (TFF) and an EXOR gate. Two orthogonal codes may be generated in a particularly simple way by one TFF.
If PSK is used in the receiving branch, an uncoded receiving channel is additionally provided. Using a TFF and an EXOR gate, the implementation of three receiving channels may therefore be possible due to the additional uncoded receiving channel.
It is useful for the delay to be controlled through digital means. These types of digital means, for example a microcontroller or a digital signal processor, are capable of delaying both the pulse repetition frequency and the PN code in a suitable way, so that the signals experience the correlation in the receiving branch.
However, it may also be advantageous if the delay is performed through circuit means. In addition to controlling the delay using digital means, it may therefore also be possible to use hardware to implement the delay.
Furthermore, it is advantageous if phase transitions are blanked. Since the switchover of the phase angle does not occur instantaneously in the real construction, errors arise after the integration of the signal. If, however, the phase-modulated signal is blanked during the transition time between the various phase angles, these errors may be minimized.
An exemplary embodiment of the present invention is based on the unexpected finding that separation of multiple receiving channels is possible through simple means. The coding of the radar sensor and the additional codings, for implementing multiple receiving channels, are separated. The additional coding has no further tasks. In this way, it is possible to design this coding very simply and to use a relatively low clock frequency. The delay of the reference signal may be necessary for the functioning of the radar is performed in the first code. The additional coding may not have to be delayed in the receiving channels due to the low clock frequency used for this purpose. Even if a very large number of channels are implemented, only a small additional outlay for components, which are clocked using a relatively low frequency, may be necessary. Only one additional modulation is necessary on the HF domain. It is also advantageous for the codes used, i.e., the first code and the additional codes for separating the receiving channels, to each be selectable independently from one another according to the respective requirements. The digital circuits for code generation and for code shifting, and the switches and mixers, may be integrated well, for example in a xe2x80x9cmonolithic microwave integrated circuitxe2x80x9d (MMIC).